Transistors within integrated circuits are becoming smaller. Each new generation of integrated circuits includes an ever increasing number of these smaller transistors. As transistors become smaller, the “leakage current” through the transistors becomes larger.
Leakage current is current that conducts through a transistor even when the transistor is supposed to be off. In most circuit configurations, leakage current is undesirable because it consumes power without producing useful work. Modern integrated circuits are experiencing larger leakage currents as a percentage of total current consumption because of the greater number of transistors, with each transistor having a larger leakage current.
Circuit techniques have been devised in attempts to reduce leakage currents. FIGS. 1A and 1B show the addition of a “sleep transistor” designed to reduce leakage current. FIG. 1A shows leakage current flowing from power supply node 102, through the transistors within circuit block 104 to reference node 106. FIG. 1A represents a circuit with large leakage currents. FIG. 1B shows sleep transistor 110 in series with the leakage current path. The sleep transistor is typically a transistor with a large threshold voltage. Turning off sleep transistor 110 when circuit block 104 is not active reduces the leakage current.
Circuit techniques can be effective to reduce leakage current, but typically require additional area on the integrated circuit die. For example, as shown in FIG. 1B, sleep transistor 110 is an addition to the circuit. For large integrated circuits, many such sleep transistors can be added resulting in considerable additional consumption of integrated circuit die area.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an alternate method and apparatus to reduce leakage current in integrated circuits.